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Consecutive cosines (Posted on 2023-12-20) Difficulty: 3 of 5
Prove

1/(cos 0 * cos 1) + 1/(cos 1 * cos 2) + ... + 1/(cos 88 * cos 89) = cos 1/sin2 1

No Solution Yet Submitted by Danish Ahmed Khan    
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observation -- probably obvious -- not a proof Comment 1 of 1
Though the puzzle doesn't mention, one can suppose by the range of values that degree measure is being used.  This is verified by doing the actual calculation in degree measure and then in radian measure:

degree measure:

tot=0; first=1;
for a=0:90-2*first
  term=1/(cosd(a)*cosd(a+first));
  tot=tot+term;
end
tot
cosd(first)/sind(first)^2
cosd(1)/sind(1)^2

The two answers agree:

ans =
          3282.63966557478
ans =
          3282.63966557478

In radians:

tot=0; first=1;
for a=0:90-2*first
  term=1/(cos(a)*cos(a+first));
  tot=tot+term;
end
tot
cos(first)/sin(first)^2
cos(1)/sin(1)^2

tot =
          2.00342661950588
ans =
          0.76305972223263

  Posted by Charlie on 2023-12-20 11:23:04
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